1. Field of the Invention
The present invention relates, in general, to reflectors used for scanning the surface of an image carrier with a laser beam in a laser beam printer, for example. In particular, the invention relates to a polygonal mirror acting as a reflector in the laser beam printer and a method for manufacturing the polygonal mirror.
2. Description of the Related Art
A conventional polygonal mirror employed by a laser beam printer may be a flat surface polygonal mirror. In the flat surface polygonal mirror, aluminum having a large specific strength or other metal materials such as an oxygen-free copper, for example, are cut by a diamond bit so that the surface of the mirror is flat. However, in recent years, to simplify the optical system of an apparatus, e.g., laser beam printer, which uses the polygonal mirror, it has been desirable to form the surface of the polygonal mirror so that it has f.theta.-lens optical characteristics. Such a mirror is described as a non-spherical polygonal mirror whose surface has a non-spherical shape, e.g., a columnar surface or a cylindroid surface. The non-spherical polygonal mirror is made similar to the above-described flat surface polygonal mirror.
However, in the above-described conventional polygonal mirror, aluminum or other metal materials, e.g., an oxygen-free copper, are processed by a diamond bit to form the surface thereof in a plano-mirror finish. To obtain the plano-mirror finished surface, a super fine processing machine is required as a machine tool and furthermore a high accuracy processing condition is required resulting in an increased production cost. In particular, in the non-spherical polygonal mirror, the surface thereof is formed in a non-spherical shape, e.g., a columnar surface, a cylindroid surface. However, it is rather difficult to process the surface of the mirror in a plano-mirror finish with a high accuracy by a machine cut. The processing cost is further increased, as compared with that of the above-described flat surface polygonal mirror.